This invention relates to suspension polymerization and more particularly to a process for producing large suspension polymer particles.
Conventional suspension polymerization processes ordinarily produce polymer particles larger than about 5 microns, and quite often between about 10 and 300 microns, and particle sizes even larger. In contrast, conventional latex polymerization process typically produce relatively small polymer particles between about 0.1 and 1 micron. With respect to extraordinarily large polymer particles, Wright patents U.S. Pat. No. 3,488,745 and U.S. Pat. No. 3,755,282 disclose methods particularly dependent upon the use of surfactants to control polymer particle size and produce large polymer beads. The prior art processes make use of persulfates, bisulfides, phosphates, sulfonate and sulfamates as surface active stabilizing agent sometimes referred to in the patents as surface active extender agents.
It now has been found that the inclusion of pentaerythritol triacrylate in the ethylenically unsaturated monomer combination copolymerized in the suspension polymerization process effectively controls and substantially increases the polymer particle size by increasing the relative amounts of pentaerythritol triacrylate. The process is a substantially improved process for substantially increasing the polymer particle size without the assistance of high levels of surface active extender agents by polymerizing the ethylenically unsaturated monomers in an aqueous medium wherein the liquid monomer combination contains minor amounts of an ethylenically unsaturated monocarboxylic acid in combination with pentaerythritol triacrylate. The resulting polymer particle size is greater than about 150 microns and preferably greater than 850 microns related to increased amounts of said triacylate. The process advantageously avoids excess amounts of extender surface active agents which help to stabilize the polymer particles but quite often detrimentally affect the physical integrity properties due to the polar groups on such surface agents and attendant water sensitivity. These and other advantages will become more apparent by referring to the Detailed Description of the Invention.